Reuse the saved_scope structures allocated by push_to_top_level

gcc/cp/ChangeLog:

	* name-lookup.c (free_saved_scope): New free list of saved_scope
	structures.
	(push_to_top_level): Attempt to reuse a saved_scope struct
	from free_saved_scope instead of allocating a new one each time.
	(pop_from_top_level_1): Chain the now-unused saved_scope structure
	onto free_saved_scope.

From-SVN: r235351

gcc/cp/ChangeLog

+2016-04-21  Patrick Palka  <ppalka@gcc.gnu.org>
+
+	* name-lookup.c (free_saved_scope): New free list of saved_scope
+	structures.
+	(push_to_top_level): Attempt to reuse a saved_scope struct
+	from free_saved_scope instead of allocating a new one each time.
+	(pop_from_top_level_1): Chain the now-unused saved_scope structure
+	onto free_saved_scope.
+
 2016-04-21  Paolo Carlini  <paolo.carlini@oracle.com>
 
 	PR c++/70540

gcc/cp/name-lookup.c

@@ -6135,6 +6135,10 @@ store_class_bindings (vec<cp_class_binding, va_gc> *names,
   timevar_cond_stop (TV_NAME_LOOKUP, subtime);
 }
 
+/* A chain of saved_scope structures awaiting reuse.  */
+
+static GTY((deletable)) struct saved_scope *free_saved_scope;
+
 void
 push_to_top_level (void)
 {
@@ -6145,7 +6149,21 @@ push_to_top_level (void)
   bool need_pop;
 
   bool subtime = timevar_cond_start (TV_NAME_LOOKUP);
-  s = ggc_cleared_alloc<saved_scope> ();
+
+  /* Reuse or create a new structure for this saved scope.  */
+  if (free_saved_scope != NULL)
+    {
+      s = free_saved_scope;
+      free_saved_scope = s->prev;
+
+      vec<cxx_saved_binding, va_gc> *old_bindings = s->old_bindings;
+      memset (s, 0, sizeof (*s));
+      /* Also reuse the structure's old_bindings vector.  */
+      vec_safe_truncate (old_bindings, 0);
+      s->old_bindings = old_bindings;
+    }
+  else
+    s = ggc_cleared_alloc<saved_scope> ();
 
   b = scope_chain ? current_binding_level : 0;
 
@@ -6238,6 +6256,11 @@ pop_from_top_level_1 (void)
   current_function_decl = s->function_decl;
   cp_unevaluated_operand = s->unevaluated_operand;
   c_inhibit_evaluation_warnings = s->inhibit_evaluation_warnings;
+
+  /* Make this saved_scope structure available for reuse by
+     push_to_top_level.  */
+  s->prev = free_saved_scope;
+  free_saved_scope = s;
 }
 
 /* Wrapper for pop_from_top_level_1.  */